The importance of histone acetylation, phosphorylation, and methylation in transcription and other DNA-mediated processes is now well established. Histones are also ubiquitylated, but in contrast to the majority of ubiquitylated proteins, ubiquitylated histones are not generally targeted for degradation and may play roles similar to those of other histone modifications. Antibodies against acetylated histones have provided unique insights into the regulation, distribution, and cellular roles of these modified histones. In this report, we describe methods to identify ubiquitylated histones in budding yeast and HeLa cells. We provide protocols to detect ubiquitylated histones that are based on a combination of in vivo genetic and immunological assays. These methods should provide relatively simple and useful tools to study the global regulation of this important but poorly understood histone modification.